1. Field of the Invention
The present invention relates to a positional difference correcting apparatus between two-route videos, which is preferable to be used for a system intending to have high reliability of the transmission by transmitting the same video to two channels.
2. Description of the Related Art
Conventionally, in a double transmission of a video designed to have high reliability, a system such that the same video is transmitted with two routes or two channels and a person monitors these two-route videos at the receiving side has been performed. In the system, in this case that a failure arises in any one of the two routes, an observer of the two-route videos detects the failure and changes over a switch to a normal channel manually.
However, according to the above described conventional art, finding an image failure and changing to a normal channel depend on manpower, so that it takes a time not less than two or three seconds from the image failure arises until a switch is changed over to the normal channel. Therefore, this involves a problem such that the video having a failure has been outputted during two or three seconds.
Accordingly, the present applicant invented an apparatus to automatically find an image failure and automatically change over a switch to a normal channel and filed the invention as a patent (namely, “an image failure detecting apparatus in a redundant double transmission” of Japanese Patent Application No. 11-156432). According to the invention, in the two-route videos to be inputted in the image failure detecting apparatus, it is assumed that the positions of the videos are identical and there is no processing delay difference.
However, in the double transmission, there are many cases such that the two-route videos pass through geographically different places, so that it is common that there is a transmission delay difference. Alternatively, in this case that a sort of a transmission apparatus to be included in respective channels, for example, a sort of an image compressing coding apparatus and a decoding apparatus or the like are different, there is a possibility that a position of an available screen in each piece of video is slightly displaced in an upper or lower direction and a right or left direction (a vertical direction and a horizontal direction) depending on an apparatus. Alternatively, in this case that one of the two channels is a satellite line, there may be a difference of about one second in the transmission time of the both channels (i.e., the difference in a time axis) and there may be a video difference of about thirty pieces between the two-route videos.